There exist a number of known systems for converting the content of cinematographic film into electrical signals for storage on video tape or for broadcast as television signals. Machines for carrying out this process, known as telecine machines, are widely available. Examples of such machines are the URSA GOLD from Cintel International Limited of Ware, Hertfordshire, England or the FDL 90 telecine manufactured by Broadcast Television Systems of Darmstadt, Germany.
A typical telecine machine comprises a film transport mechanism which transports a length of film at a constant predetermined rate of typically 24 or 30 frames per second past a scanning system. The frame rate at which the film is transported is the telecine machine is the rate at which the film frames are replayed for real time viewing of the film, i.e the real time frame rate. The scanning system produces electrical signals corresponding to the content of the film which are then processed to give television signals which may be recorded on video tape or directly broadcast. A number of scanning systems are available; for example the scanning system in the URSA GOLD uses a cathode ray tube to produce a flying spot of light, the position of which may be controlled by a digitally addressable scanning system. In this system, the light from the flying spot transmitted by the film is detected by a number of photomultiplier tubes which convert the intensity of the light into a corresponding electrical signal.
An alternative scanning system is that used for example in the FDL 90, which comprises a linear array of charge coupled devices (CCDs) which record the light transmitted by the film at points in a line spanning the film frame and orientated transverse to the transport direction. The movement of the film past the CCD array by the transport mechanism allows the CCD array to scan the whole length of the film.
The above two examples of telecine machines operate in Standard Definition, in common with the vast majority of broadcast television and video tape systems. This terminology is used, in Europe, to describe a picture format consisting of 625 picture lines, 576 of which are active, each line comprising 720 picture samples, the repetition rate being 25 frames per second, which is equivalent to 50 fields per second. In North America, the Standard Definition format is defined by 525 picture lines, of which 486 are active, each comprising 720 picture samples with a repetition rate of 30 frames (60 fields) per second. The standards are documented in Recommendation 601 of the CCIR, ratified at the 16th Plenary Assembly in Dubrovnik in 1986. The sampling frequency for European Standard Definition television data is 13.5 MHz resulting in a raw data stream of 260 megabits per second.
Other telecine machines exist, such as the MK III HD from Cintel International Limited or the FLH-1000 from Broadcast Television Systems, which produce High Definition television signals. High Definition television is a standard which has not yet been widely introduced for television broadcasts but is in various stages of development and prototype trial. The proposed European standard is for a system of 1250 lines of which 1152 are active, each comprising 1920 picture samples with a repetition rate of 25 frames (50 fields) per second. Thus, the sampling frequency of this system is 72 MHz resulting in a raw data stream of 1152 megabits per second. Thus the ratio of the data rates of high definition telecine systems to standard definition telecine systems is 16:3 (5.33) and thus the data rate of high definition systems is typically in excess of 5 times that of standard definition.
In order to allow existing standard definition telecine machines to produce high definition television signals there have been proposed a number of systems for producing high definition signals from standard definition systems. An example of such a system is disclosed in GB-A-2243264 (Rank Cintel Limited). According to this system each film frame is repetitively scanned to produce a plurality of interlaced scans. Each interlaced scan can be processed by a standard definition processing system at a standard definition data rate of 216 megabits per second, which requires no increase in bandwidth of the standard definition processing apparatus. The scans are combined to produce a high definition signal. Of course, the data content of a high definition picture is 5.33 times larger than that of a standard definition picture and thus it takes 5.33 times longer for this system to produce a high definition signal than it would to produce a standard definition signal from the same film frame.
It is customary to operate telecine machines in a real time mode such that the resultant signals are produced at the broadcast data rate. Thus according to the system of GB-A-2243264, it takes 5.33 times longer than real time to transfer a given piece of programme material from film to video or into broadcast signals at high definition. For example, a three hour piece of film will take 16 hours to transfer.
As mentioned above, the high definition television standard is currently at a prototype stage and thus there is little demand for the transfer of film material into high definition television signals because of the limited distribution channels that are currently available. Commercially, telecine apparatus is expensive both to buy and to hire, particularly in the case of telecine apparatus that can operate at the high definition data rate of 1152 megabits per second. In order to increase the utilisation, and therefore the revenue gained from, a high definition telecine machine certain manufacturers offer the facility of producing standard definition signals from a high definition telecine machine. This is usually achieved by scanning the film material at the high definition sampling rate and averaging down the resultant data to produce a standard definition signal. Of course, the use of a telecine machine capable of producing high definition signals to produce signals at standard definition is financially disadvantageous, as the price and running costs of a high definition system are typically three times that of a standard definition system, yet the financial return from a high definition system operating in this mode will only be equivalent to that from a cheaper standard definition machine.